The present invention relates to new species of lactic acid bacteria belonging to the genus Streptococcus.
The identification of lactic acid bacteria is essential in the dairy industry, and consists in differentiating distinctive morphological, physiological and/or genetic characteristics between several species.
The distinctive physiological characteristics for a given species of lactic acid bacteria may be determined by various tests including, for example, analyzing their capacity to ferment various sugars and the migration profile of total proteins on an SDS-PAGE type electrophoresis gel (Pot et al., Taxonomy of lactic acid bacteria, in Bacteriocins of lactic acid bacteria, Microbiology, Genetics and Applications, L. De Vuyst, and E. J. Vandamme ed., Blackie Academic and Professional, London, 1994).
The migration profile of the total proteins of a given species, determined by SDS-PAGE gel electrophoresis, when compared, with the aid of a densitometer, with other profiles obtained from other species, makes it possible to determine the taxonomic relationships between the species. Numerical analysis of the various profiles, for example, with the GelCompar(copyright) software, makes it possible to establish the degree of correlation between the species which is a function of various parameters, in particular of the algorithms used (GelCompar, version 4.0, Applied Maths, Kortrijk, Belgium; algorithms: xe2x80x9cPearson Product Moment Correlation Coefficient, Unweighted Pair Group Method Using Average Linkagexe2x80x9d).
To date, comparative analysis of the total protein profile by SDS-PAGE gel electrophoresis has been thoroughly tested as an effective means for distinguishing between homogeneous and distinct groups of species of lactic acid bacteria (Pot et al., Chemical Methods in Prokaryotic Systematics, Chapter 14, M. Goodfellow, A. G. O""Donnell, Ed., John Wiley and Sons Ltd, 1994).
With this SDS-PAGE method, the preceding experiments have thus shown that when a degree of Pearson correlation of more than 78 (on a scale of 100) is obtained between two strains of lactic acid bacteria, it is justifiably possible to deduce therefrom that they belong to the same species (Kersters et al., Classification and Identification methods for lactic bacteria with emphasis on protein gel electrophoresis, in Acid Lactic Bacteria, Actes du Colloque Lactic ""91, 33-40, Adria Normandie, France, 1992; Pot et al., The potential role of a culture collection for identification and maintenance of lactic acid bacteria, Chapter 15, pp. 81-87, in: The Lactic Acid Bacteria, E. L. Foo, H. G. Griffin, R. Mollby and C. G. Heden, Proceedings of the first lactic computer conference, Horizon Scientific Press, Norfolk).
By way of example, it was recently possible to divide the group of acidophilic lactic acid bacteria into 6 distinct species by means of this technique (Pot et al., J General Microb., 139, 513-517, 1993). Likewise, this technique was recently used to establish, in combination with other techniques, the existence of several new species of Streptococcus, such as Streptococcus dysgalactiae subsp. equisimilis, Streptococcus hyovaginalis sp. nov. and Streptococcus thoraltensis sp. nov (Vandamme et al., Int. J. Syst. Bacteriol., 46, 774-781, 1996; Devriese et al., Int. J. Syst. Bacteriol., 1997, In press).
The identification of new species of lactic acid bacteria cannot however be reduced to a purely morphological and/or physiological analysis of the bacteria. Indeed, two species which are very closely related morphologically and/or physiologically may be distantly related from a genetic point of view. Analysis of the 16S ribosomal RNA of the lactic acid bacteria is thus of vital importance for determining definitively if a lactic acid bacterium belongs to a known genus or species.
To date, the xe2x80x9cDeutsche Sammlung Von Mikroorganismen und Zellkulturen GmbHxe2x80x9d (DSM, Braunschweig, Germany) has officially recorded about 48 different species belonging to the genus Streptococcus (see the list below). All these species possess a 16S ribosomal RNA which is typical of the genus Streptococcus, and may be divided into distinct and homogeneous groups by means of the SDS-PAGE technique mentioned above.
The present invention relates to the identification, by means of the techniques presented above, of a new species of lactic acid bacterium belonging to the genus Streptococcus, and to its use in the dairy industry in general.
The invention relates to any lactic acid bacterium, whose 16S ribosomal RNA is characteristic of the genus Streptococcus; and whose total protein profile, obtained after migration of the total proteins on an SDS-PAGE electrophoresis gel, is characteristic of that of the strain of lactic acid bacterium CNCM I-1920, but distinct from those of the recognized species belonging to the genus Streptococcus, namely S. acidominimus, S. agalactiae, S. alactolyticus, S. anginosus, S. bovis, S. canis, S. caprinus, S. constellatus, S. cricetus, S. cristatus, S difficile, S. downei, S. dysgalactiae ssp. dysgalactiae, S. dysgalactiae ssp. equisimilis, S equi, S. equi ssp. equi, S equi ssp. zooepidemicus, S. equinus, S. ferus, S. gallolyticus, S gordonii, S. hyointestinalis, S. hyovaginalis, S. iniae, S. intermedius, S intestinalis, S. macacae, S. mitis, S. mutans, S. oralis, S. parasanguinis, S. parauberis, S. phocae, S. pleomorphus, S. pneumoniae, S. porcinus, S pyogenes, S. ratti, S. salivarius, S. sanguinis, and shiloi, S sobrinus, S. suis, S thermophilus, S. thoraltensis, S. uberis, S. vestibularis, S. viridans. 
The invention further relates to the use of a strain of lactic acid bacterium according to the invention for the preparation of a dietary composition, in particular an acidified milk or a fromage frais, for example.
The invention also relates to the use of a polysaccharide, capable of being secreted by a lactic acid bacterium according to the invention, which consists of a chain of glucose, galactose and N-acetylglucosamine in a respective proportion of 3:2:1, for the preparation of a dietary or pharmaceutical composition.
The subject of the invention is a dietary or pharmaceutical composition comprising a strain of lactic acid bacterium according to the invention.
Finally, the subject of the invention is also a dietary or pharmaceutical composition comprising a polysaccharide consisting of a chain of glucose, galactose and N-acetylglucosamine in a respective proportion of 3:2:1.